1. Field of the Invention
The present invention pertains to a method and apparatus for updating portions of a write once/read many memory and for creating and updating self-describing file headers for data files stored on the memory. More particularly, the present invention relates to a method and apparatus for reducing the amount of data to be updated in a write once/read many memory card directory by providing a self-describing file header for each file within the write once/read many memory.
2. Description of the Related Art
With recent advances in technology, the storage capacity of write once/read many memory media has increased to a point where those media have become quite efficient and popular for storing various types of data. More specifically, write once/read many media such as optical memory cards are widely used to store text data, binary data, voice entry data, image data, and other multimedia data for many different applications. The health industry in particular has taken advantage of the various data storage capabilities of optical memory cards and has found that optical memory cards are convenient media for storing x-rays, patient text history, and voice commentary.
In addition to its ability to store multimedia data, an optical memory card has become popular because of its high density capacity for storing data and because it is a non-volatile medium for storing data thereon. The write once feature ensures that data once placed on the card cannot physically be deleted. This is of great value in preventing loss of data stored on these media.
Another feature of the optical memory card is its size. Generally, the size of the optical memory card is no larger than a standard credit card and therefore data stored on the card is easily transportable. For example, a patient may carry his/her medical history in a wallet or purse and deliver the medical history to a lab or a physician for review and update. The size of the card makes it also convenient to enter data onto the optical memory card at a physician's office or at a lab using a personal computer work station.
The full benefit of using write once/read many media such as optical cards has not heretofore been realized, however, because software programs interact with the media as if the media were a conventional floppy disk drive. For example, writes and reads are handled in a similar fashion as writes and reads to a floppy disk. But, treating an optical memory card as a floppy disk treats the card inefficiently because of physical differences between the mediums. For example, a floppy disk is a write many/read many medium whereas the optical memory card is a write once/read many medium. As a result, storage capacity on the optical memory card is wasted since interim file directories and data that are written to a floppy disk must be re-written each time on the optical memory card since the optical card is a write once medium. In some systems, the problem with emulating a floppy disk is that 344 bytes on the optical memory card are not addressed using some types of DOS floppy disk drives since those drives format a disk with 1,024 bytes per track rather than 1,368 bytes per track for an optical memory card.
Thus, it has not been considered possible to make updates to an optical memory card without having to rewrite an entire directory or a file to unwritten locations in the optical memory card. Consequently, conventional use of an optical memory card does not allow a user to utilize the storage space on an optical memory card to its fullest capacity since much of the card is used for rewriting directory information and updated files every time a revision is made, and much of the available bytes per track is not even accessible.